Here are two images of audio consoles at 111 Sutter Street. Both images are probably from the late 1930s.
LEFT: Engineer Frank Fullaway is mixing a remote broadcast, as evidenced by the labels over the mixers, which indicate "Mission Dolores", "Studio Announcer", and "Opera House". The name of the engineer and the location is unknown, but the "VU" meter has been added to the microphone mixer, meaning it dates to an earlier era. Also, the knobs below each fader are labelled "microphone current", indicating they were designed to be used with carbon microphones, which required an external voltage source. Carbon microphones ceased to be used in the mid 1930's when ribbon microphones such as the RCA 44A (at left) became available.
RIGHT: Engineer George Greaves looks over a new audio
console in an announcer's studio. The three mixer knobs are
labeled "Program", "Announce" and "Master". Typically, this kind
of equipment at NBC was custom-made for the network.